The invention relates to a water-dilutable coating agent for preparing the base layer of a multilayer coating and which contains pigments, if desired, flow-control agents, thixotroping agents, fillers, organic solvents and other customary auxiliaries, and to a process for preparing a multilayer coating.
It is known in particular in the coating of motor cars but also in other areas where coatings are desired which have a good decorative effect and at the same time good corrosion protection, to provide substrates with several coating layers which are arranged on top of one another. In this method, a pigmented coating agent is first applied, followed by a transparent topcoat, i.e. as a rule a clear coating, which does not contain any or only transparent pigments.
Metallic pigments which lead to metallic coatings are frequently used in the base layer. The automotive industry has hitherto used in the coating of motor cars conventional coating agents, which have a high organic solvent content. For economic reasons, and to reduce environmental pollution, there is a trend to avoid, as far as possible, organic solvents in coating compositions.
For this reason coating agents have been disclosed which predominantly contain water as the solvent or dispersant and which contain only small amounts of organic solvents. For instance, German Offenlegungsschrift No. 2,926,584 describes an aqueous binder mixture for preparing metallic base coats, which contains as binder a water-soluble condensation product of a polyester, a polycarboxylic acid mixture containing trimelitic acid, an epoxidized oil and basic compounds.